Pentagon Stone Memorial EarthCache

This is an Earthcache — there is no physical cache to be found here. Instead, you will partake in a geology lesson. Read the cache description and make observations at the Pentagon Stone Memorial. Complete the listed logging requirements to get credit for this cache.

This memorial is located on the grounds of the National Museum of the United States Army (NMUSA) and is NOT available 24/7. NMUSA is open daily from 0900 - 1700 (except for December 25th).

This memorial recognizes the loss of life that occurred when terrorists hijacked American Airlines Flight 77 and crashed it into the Pentagon on September 11, 2001.

When the Pentagon was built in 1941, its exterior was faced with Indiana Limestone. These three panels, which were recovered in the aftermath of the attack, once displayed evidence of the plane's explosion, as well as the resulting fire and smoke damage. The 125 lives lost inside the Pentagon might have been greater, had it not been for the strength of the building's construction.

Indiana limestone is a sedimentary rock that is found in the Salem Formation, a geological formation that is prominent in south central Indiana near Bedford, Indiana. It formed in a coastal ecosystem under a process called lithification.

Lithification is defined as the process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock. It is also an oolitic limestone, which is named for its layers of bead-like spheres of calcium mineralized microbes known as ooids.

Limestone is primarily made up of calcium carbonate (CaCO3). That is because it was deposited as marine fossils (many marine organisms have skeletons that are primarily made of calcium) and decomposed at the bottom of a shallow inland sea. This Limestone also contains variable amounts of silica in the form of jasper or flint. In addition, this Limestone contains small amounts of clay, silt, and sand which are visible as disseminations, nodules, or layers within the rock.

Over 350 million years ago, most of the present-day Midwestern United States was covered by a tropical sea during the Mississippian Period. Those waters were shallow enough for the waves to move coarse carbonate sand across the seafloor. This constant wave action broke the larger fossils down, and washed the smaller ones away. As layers built up on top of other layers, pressure was formed. Over time, the accumulated debris remained under pressure until they solidified into limestone.

Limestone from Indiana is designated as an Oolitic Limestone, which is a carbonate rock made up of mostly ooids (sand-sized carbonate particles that have concentric rings of CaCO3). It was previously believed that these rings formed around grains of sand or shell fragments that were rolled around on the shallow sea floor. More recently, scientists discovered that ooids were made of concentric layers of mineralized microbes that lived about 200 million years ago, during the Jurassic Period when dinosaurs still walked on Earth.

LOGGING REQUIREMENTS:

To log this Earthcache, read the geology lesson above and make observations at the Pentagon Stone Memorial. Answer the questions below and send the answers to me via email OR by sending an instant message through my geocaching profile.

QUESTION 1. What is the process called when sediment layers are turned to rock?

QUESTION 2. Look closely at the stone. Do you see the grains that make up the stone? What colors do you see?

QUESTION 3. Touch the stone. Do the grains feel tightly cemented together or do they feel loose?

OPTIONAL: If you’re willing to do so, please share your September 11th story. Where were you on that frightful day? What do you remember? How were you and your family affected? I know this can be a very sensitive and personal topic, so this is completely OPTIONAL. Tell your story in your “Found It” log or with the answers you send me in a separate message. Once again, this is totally up to you.

OPTIONAL: Post a photo that readily indicates that you (and anyone else logging the find) were physically at the location.

REFERENCES:

1. Funding sought for more work at Red Run Park’s 9-11 Tribute in Rouzerville, Zach Glenn, The Record Herald, February 25, 2014, therecordherald.com

2. The Pentagon 75 Years, Building an Icon, Dwight Jon Zimmerman, Faircount Media Group, 2018, Pg. 35 - 41, issuu.com

3. BUILDING THE NATION, Indiana Limestone Company, indianalimestonecompany.com

4. Indiana Limestone: A Short Biography, Geohistories, Phoebe Cohen, Co-Evolution of Earth and Life, Williams College, January 29, 2015, sites.williams.edu

5. Pentagon Stones Host Mineralized Microbes Older Than the Dinosaurs, Brooks Hays, Science News, January 19, 2018, upi.com

6. The Pentagon, Jeff Swiatek, virginiaplaces.org

7. A Limestone Block From the Pentagon, Earthcache by Awesnap, October 6, 2020, geocaching.com